U.S. patent number 8,106,656 [Application Number 12/949,505] was granted by the patent office on 2012-01-31 for superconducting loop, saddle and birdcage mri coils.
This patent grant is currently assigned to The University of Houston System. Invention is credited to Krzysztof Nesteruk, Jaroslaw Wosik, Lei Ming P Xie.
United States Patent |
8,106,656 |
Wosik , et al. |
January 31, 2012 |
Superconducting loop, saddle and birdcage MRI coils
Abstract
New MRI coil and resonators are disclosed based solely on
superconducting inductive element and built-in capacitive elements
as well as hybrid superconducting-metal inductive and capacitive
elements having superior SNR. Single and multiple small animal MRI
imaging units are also disclosed including one or more resonators
of this invention surrounding one or more small animal cavities.
Methods for making and using the MRI coils and/or arrays are also
disclosed.
Inventors: |
Wosik; Jaroslaw (Houston,
TX), Nesteruk; Krzysztof (Warsaw, PL), Xie; Lei
Ming P (Houston, TX) |
Assignee: |
The University of Houston
System (Houston, TX)
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Family
ID: |
34860183 |
Appl.
No.: |
12/949,505 |
Filed: |
November 18, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110124507 A1 |
May 26, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10583625 |
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7859264 |
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PCT/US2005/001813 |
Jan 20, 2005 |
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60537782 |
Jan 20, 2004 |
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Current U.S.
Class: |
324/318; 324/309;
324/321; 324/307 |
Current CPC
Class: |
G01R
33/34007 (20130101); G01R 33/3415 (20130101); G01R
33/34046 (20130101); G01R 33/34023 (20130101) |
Current International
Class: |
G01V
3/00 (20060101) |
Field of
Search: |
;324/300-322
;382/128-131 ;600/407-435 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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42 18 635 |
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Dec 1993 |
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DE |
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0 895 092 |
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Feb 1999 |
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EP |
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1 251 361 |
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Oct 2002 |
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EP |
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2616911 |
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Dec 1988 |
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FR |
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WO 93/24848 |
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Dec 1993 |
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WO |
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WO 00/70356 |
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Nov 2000 |
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WO |
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Other References
Wosik et al. Jul. 10, 2003 A Novel planar design of 200 MH
superconducting array. cited by examiner .
Chow et al Jul. 10, 2003 A two-channel HTS thin-film phased array
coil for low field MRI. cited by examiner .
Malagoli et al Oct. 2002 Radiofrequency response of Ag-sheilded . .
. superconducting tapes. cited by examiner.
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Primary Examiner: Koval; Melissa
Assistant Examiner: Fetzner; Tiffany
Attorney, Agent or Firm: Strozier; Robert W.
Parent Case Text
RELATED APPLICATIONS
The present application is a divisional application of U.S. patent
application Ser. No. 10/583,625, filed Jun. 20, 2006, which is a 35
U.S.C. .sctn.371 National Phase Application of PCT Application
Serial No. PCT/US05/01813, filed Jan. 20, 2005, published as
WO/2005/078468 on Aug. 25, 2005, which claims the benefit of and
provisional priority to U.S. Provisional Patent Application Ser.
No. 60/537,782 filed Jan. 20, 2004, the entire contents of which is
are hereby incorporated by reference under operation of the final
paragraph of the specification.
Claims
We claim:
1. An MRI coil apparatus comprising: four strips, each strip
comprising a superconducting layer, where the strips are arranged
to form a closed loop having four overlapping regions, each region
comprising end portions of two different strips, and separating
dielectric layers interposed between the superconducting layers at
the overlapping regions in order to form built-in capacitors,
wherein two of the strips are straight and two of the strips are
curvilinear.
2. The MRI coil apparatus of claim 1, wherein each strip further
comprises a substrate dielectric layer, where the strips are
oriented with all of the superconducting layers facing in one
direction or where opposite pairs of strips are oriented with their
respectively superconducting layers facing in opposite
directions.
3. The MRI coil apparatus of claim 2, wherein the substrate
dielectric layers are rigid.
4. The MRI coil apparatus of claim 2, wherein the substrate
dielectric layers associated with the straight legs are rigid and
the substrate dielectric layers associated with the curvilinear
legs are flexible.
5. The MRI coil apparatus of claim 2, further comprising: a metal
layer formed on at least one exposed outer portion of a substrate
dielectric layer in order to form coupling or decoupling capacitive
elements.
6. The MRI coil apparatus of claim 1, wherein two of the strips are
straight and two of the strips are arcuate.
7. The MRI coil apparatus of claim 2, wherein the substrate
dielectric layers are the separating dielectric layers.
8. The MRI coil apparatus of claim 1, further comprising: a metal
layer formed on at least one exposed outer portion of a dielectric
layer formed on an exposed outer portion of at least one of the
superconducting layers in order to form coupling or decoupling
capacitive elements.
9. The MRI coil apparatus of claim 8, further comprising: wires
bonded to the metal layers, where the metal wires are arranged to
connect the apparatus to a pre-amplifier.
10. A hybrid MRI coil apparatus comprising: Two superconducting
strips, each superconducting strip comprising a superconducting
layer, two metal strips, and separating dielectric layers, where
the superconducting strips and the metal strips are arranged to
form a closed loop having four overlapping regions, each region
comprising end portions of one superconducting strip and one metal
strip and where the separating dielectric layers are interposed
between the superconducting layers and the metal strips at the
overlapping regions in order to form built-in capacitors.
11. The hybrid MRI coil apparatus of claim 10, wherein each
superconducting strip further comprises a substrate dielectric
layer, where the strips are oriented with all of the
superconducting layers facing in one direction or where opposite
pairs of strips are oriented with their respectively
superconducting layers facing in opposite directions.
12. The hybrid MRI coil apparatus of claim 11, further comprising:
a metal layer formed on at least one exposed outer portion of a
substrate dielectric layer in order to form coupling or decoupling
capacitive elements.
13. The hybrid MRI coil apparatus of claim 11, wherein the
substrate dielectric layers are rigid.
14. The hybrid MRI coil apparatus of claim 11, wherein two of the
substrate dielectric layers are rigid and two of the substrate
dielectric layers are flexible.
15. The hybrid MRI coil apparatus of claim 11, wherein the
substrate dielectric layers are the separating dielectric
layers.
16. The hybrid MRI coil apparatus of claim 10, further comprising:
a metal layer formed on at least one exposed outer portion of a
dielectric layer formed on an exposed outer portion of at least one
of the superconducting layers in order to form coupling or
decoupling capacitive elements.
17. The hybrid MRI coil apparatus of claim 16, further comprising:
wires bonded to the metal layers, where the wires are arranged to
connect the apparatus to a pre-amplifier.
18. A birdcage-type resonator apparatus comprising: a plurality of
coil apparatuses, where each coil apparatus includes: four strips,
each strip comprises a superconducting layer, where the strips are
arranged to form a closed shape having four overlapping regions,
each region comprising end portions of two different strips, and
separating dielectric layers interposed between the superconducting
layers at the overlapping regions in order to form built-in
capacitors, and at least one small animal cavity, where the coil
apparatuses are arranged around the cavity in order to permit MRI
imaging of an animal placed within the cavity and where two of the
strips are straight and two of the strips are curvilinear.
19. The birdcage-type resonator apparatus of claim 18, wherein each
strip further comprises a substrate dielectric layer.
20. The birdcage-type resonator apparatus of claim 19, wherein the
substrate dielectric layers are rigid.
21. The birdcage-type resonator apparatus of claim 19, wherein two
of the substrate dielectric layers are rigid and two of the
substrate dielectric layers are flexible.
22. The birdcage-type resonator apparatus of claim 18, wherein two
of the strips are straight and two of the strips are arcuate.
23. The birdcage-type resonator apparatus of claim 19, wherein the
substrate dielectric layers are the separating dielectric
layers.
24. The birdcage-type resonator apparatus of claim 18, further
comprising: a metal layer formed on at least one exposed outer
portion of a dielectric layer formed on an exposed outer portion of
at least one of the superconducting layers in order to form
coupling or decoupling capacitive elements.
25. The birdcage-type resonator apparatus of claim 24, further
comprising: wires bonded to the metal layers, where the wires are
arranged to link a plurality of the coil apparatuses together in
order to form arrays or in order to connect the coil apparatuses to
at least one pre-amplifier.
26. The birdcage-type resonator apparatus of claim 19, further
comprising: a metal layer formed on at least one exposed outer
portion of a substrate dielectric layer in order to form coupling
or decoupling capacitive elements.
27. A birdcage-type resonator apparatus comprising: a plurality of
coil apparatuses including: two superconducting strips, each
superconducting strip including: at least one superconducting
layer, two metal strips, and separating dielectric layers, and at
least one small animal cavity, where the coil apparatuses are
arranged around the cavity in order to permit MRI imaging of an
animal placed within the cavity and where the superconducting
strips and the metal strips are arranged in order to form a closed
shape having four overlapping regions, each region comprising end
portions of one superconducting strip and one metal strip and where
the separating dielectric layers are interposed between the
superconducting layers and the metal strips at the overlapping
regions in order to form built-in capacitors.
28. The birdcage-type resonator apparatus of claim 27, wherein each
superconducting strip further comprises a substrate dielectric
layer.
29. The birdcage-type resonator apparatus of claim 28, wherein the
substrate dielectric layers are rigid.
30. The birdcage-type resonator apparatus of claim 28, wherein two
of the substrate dielectric layers are rigid and two of the
substrate dielectric layers are flexible.
31. The birdcage-type resonator apparatus of claim 28, wherein the
substrate dielectric layers are the separating dielectric
layers.
32. The birdcage-type resonator apparatus of claim 27, further
comprising: a metal layer formed on at least one exposed outer
portion of a dielectric layer formed on an exposed outer portion of
at least one of the superconducting layers in order to form
coupling or decoupling capacitive elements.
33. The birdcage-type resonator apparatus of claim 32, further
comprising: wires bonded to the metal layers, where the metal wires
are arranged to link a plurality of the coil apparatuses together
in order to form arrays or in order to connect the coil apparatuses
to at least one pre-amplifier.
34. The birdcage-type resonator apparatus of claim 28, further
comprising: a metal layer formed on at least one exposed outer
portion of a substrate dielectric layer in order to form coupling
or decoupling capacitive elements.
35. A small animal MRI apparatus comprising: a vacuum housing
including at least one cylindrical cavity configured to receive a
small animal, a coolant reservoir including a coolant, a coolant
inlet, a coolant outlet and a cold plate forming an internal end of
the reservoir, a resonator comprising: a plurality of coil
apparatuses each including: two superconducting strips, each strip
including at least one superconducting layer, two metal strips, and
separating dielectric layers, and where the resonator forms a
cavity in order to permit MRI imaging of an animal placed within
the cavity and where the superconducting strips and the metal
strips are arranged to form an elongated closed shape having four
overlapping regions and the separating dielectric layers are
interposed between the superconducting layers and the metal strips
at the overlapping regions, each region comprising end portions of
one superconducting strip and one metal strip in order to form
built-in capacitors and where the coil apparatuses are arranged
about the cavity.
36. The small animal MRI apparatus of claim 35, wherein each
superconducting strip further comprises a substrate dielectric
layer.
37. The small animal MRI apparatus of claim 35, wherein the
substrate dielectric layers are rigid.
38. The small animal MRI apparatus of claim 35, wherein the
substrate dielectric layers are the separating dielectric
layers.
39. The small animal MRI apparatus of claim 35, further comprising:
a metal layer formed on at least one exposed outer portion of a
dielectric layer formed on an exposed outer portion of at least one
of the superconducting layers in order to form coupling or
decoupling capacitive elements.
40. The small animal MRI apparatus of claim 39, further comprising:
wires bonded to the metal layers, where the wires are arranged to
link a plurality of the coil apparatuses together in order to form
arrays or in order to connect the apparatus to at least one
pre-amplifier.
41. The small animal MRI apparatus of claim 36, further comprising:
a metal layer formed on at least one exposed outer portion of a
substrate dielectric layer in order to form coupling or decoupling
capacitive elements.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the general field of magnetic
resonance, and to methods and apparatus for their practice.
More particularly, the present invention relates to an apparatus
and a method for using the apparatus, where the apparatus includes
a housing including at least one cavity for housing a small mammal,
where the housing includes a superconducting array of MRI elements
cooled by liquid nitrogen and where the housing with an animal
therein is designed to place in an MRI instrument and MRI images of
the mammal obtained.
2. Description of the Related Art
It is known that in magnetic resonance imaging (MRI) when receiving
signal coil noise dominates, overall system noise, using
superconducting receiving coil, increases significantly as does
overall signal-to-noise ratio of the MRI system. Superconducting
coils in either surface coil or volume coil configuration are
formed out of four or more sections of dielectric/superconductor or
dielectric/metal strips. Strips are made out of thin high
temperature superconducting (HTS) or metal thin films deposited on
dielectric rigid or flexible substrates. Such strips are connected
together via build-in capacitors. At each of the connections, YBCO
layers are separated by dielectric layers to form capacitors.
Resonant frequency is determined mainly by a length of the
structure and a thickness of the dielectric layer separating the
YBCO layers and a dielectric constant of the dielectric layer. Flat
surface coils, saddle coils and volume birdcage coils have been
designed.
Birdcage radio frequency coils have been widely used in magnetic
resonance imaging because of their efficiency and azimuthal B1
field homogeneity and design of all superconducting birdcage for
small animals has a practical potential. Thus, there is a need in
the art for efficient small animal including small mammal MRI
birdcage devices that have low noise and/or improved
signal-to-noise ratios and have the capability of simultaneously
housing multi-animals in a single device.
SUMMARY OF THE INVENTION
The present invention provides a MRI single coil including
composite structures of dielectric layers and superconducting
layers and/or metallic layers, where the layers are constructed to
form inductive regions of the superconducting layers and/or
metallic layers interconnected by capacitive regions formed by
superconducting layers and/or metallic layer having a dielectric
layer interposed therebetween.
The present invention provides a MRI phased array of coils of this
invention constructed in such a way as to form MRI housings
including a single animal tube or multiple animal tubes, each tube
having one or more MRI arrays associated therewith.
The present invention also provides a multi-animal apparatus
adapted for simultaneous measurements of multi-animals, where the
apparatus includes a plurality of animal tubes, each tube including
one or more MRI coils or coil arrays of this invention. In one
preferred embodiment, each animal tube includes a birdcage-like MRI
coil array. The apparatus also includes a cryogenic system for
cooling the MRI coils or MRI coil arrays.
The present invention also provides an MRI resonator apparatus
comprising four superconducting members, each member including a
superconducting layer, where the members arranged to form a closed
shape having four overlapping regions, and separating dielectric
layers interposed between the superconducting layers at the
overlapping regions to form built-in capacitors. Each member
comprises a substrate dielectric layer upon which the
superconducting layer was formed. The substrate dielectric layers
can be rigid. Two of the substrate dielectric layers can be rigid
and two of the substrate dielectric layers can be flexible. The
members are straight. Two of the members can be straight and two of
the members can be curvilinear. Two of the members can be straight
and two of the members can be arcuate. The substrate dielectric
layers can be the separating dielectric layers. The apparatus can
further comprise a metal layer formed on an exposed portion of a
dielectric layer or a external dielectric layer formed form on an
exposed portion of a superconducting layer with a metal layer
formed on the outer surface of the external dielectric layer to
form coupling or decoupling capacitive elements. The apparatus can
further comprise wires bonded to the metal layers, where the metal
wires are adapted to link a plurality of the apparatus together to
form arrays or to connect the apparatus to a pre-amplifier.
The present invention also provides a hybrid MRI resonator
apparatus comprising two superconducting members, each member
including a superconducting layer, two metal member, and separating
dielectric layers, where the superconducting members and the metal
members are arranged to form a closed shape having four overlapping
regions and the separating dielectric layers are interposed between
the superconducting layers and the metal members at the overlapping
regions to form built-in capacitors. Each superconducting member
comprises a substrate dielectric layer upon which the
superconducting layer was formed. The substrate dielectric layers
can be rigid. Two of the substrate dielectric layers can be rigid
and two of the substrate dielectric layers can be flexible. The
superconducting members can be straight or curvilinear or arcuate.
The substrate dielectric layers can be the separating dielectric
layers. The apparatus can further comprise a metal layer formed on
an exposed portion of a dielectric layer or a external dielectric
layer formed form on an exposed portion of a superconducting layer
with a metal layer formed on the outer surface of the external
dielectric layer to form coupling or decoupling capacitive
elements. The apparatus can further comprise wires bonded to the
metal layers, where the metal wires are adapted to link a plurality
of the apparatus together to form arrays or to connect the
apparatus to a pre-amplifier.
The present invention provides a birdcage-type resonator apparatus
comprising a plurality of coils apparatus including four members,
each member including a superconducting layer, where the members
arranged to form a closed shape having four overlapping regions,
and separating dielectric layers interposed between the
superconducting layers at the overlapping regions to form built-in
capacitors, and at least one small animal cavity, where the coil
apparatus are arranged around the cavity to permit MRI imaging of
an animal placed within the cavity. Each member comprises a
substrate dielectric layer upon which the superconducting layer was
formed. The substrate dielectric layers can be rigid. Two of the
substrate dielectric layers can be rigid and two of the substrate
dielectric layers can be flexible. The members can be straight. Two
of the members can be straight and two of the members can be
curvilinear. Two of the members can be straight and two of the
members can be arcuate. The substrate dielectric layers can be the
separating dielectric layers. The apparatus further comprises a
metal layer formed on an exposed portion of a dielectric layer or a
external dielectric layer formed form on an exposed portion of a
superconducting layer with a metal layer formed on the outer
surface of the external dielectric layer to form coupling or
decoupling capacitive elements. The apparatus further comprises
wires bonded to the metal layers, where the metal wires are adapted
to link a plurality of the apparatus together to form arrays or to
connect the apparatus to a pre-amplifier.
The present invention also provides a birdcage-type resonator
apparatus comprising a plurality of coils apparatus including two
superconducting members, each member including a superconducting
layer, two metal member, and separating dielectric layers, and at
least one small animal cavity, where the coil apparatus are
arranged around the cavity to permit MRI imaging of an animal
placed within the cavity and where the superconducting members and
the metal member are arranged to form a closed shape having four
overlapping regions and the separating dielectric layers are
interposed between the superconducting layers and the metal members
at the overlapping regions to form built-in capacitors. Each
superconducting member comprises a substrate dielectric layer upon
which the superconducting layer was formed. The substrate
dielectric layers can be rigid. Two of the substrate dielectric
layers can be rigid and two of the substrate dielectric layers can
be flexible. The superconducting members can be straight. The
superconducting members can be curvilinear. The superconducting
members can be arcuate. The substrate dielectric layers can be the
separating dielectric layers. The apparatus further comprises a
metal layer formed on an exposed portion of a dielectric layer or a
external dielectric layer formed form on an exposed portion of a
superconducting layer with a metal layer formed on the outer
surface of the external dielectric layer to form coupling or
decoupling capacitive elements. The apparatus further comprises
wires bonded to the metal layers, where the metal wires are adapted
to link a plurality of the apparatus together to form arrays or to
connect the apparatus to a pre-amplifier.
The present invention also provides a small animal MRI apparatus
comprising a vacuum housing including at least one cylindrical
cavity adapted to receive a small animal, a coolant reservoir
including a coolant, a coolant inlet, a coolant outlet and a cold
plate forming an internal end of the reservoir, a resonator of this
invention surrounding each cavity or a plurality of coils of this
invention positioned within the housing to permit MRI imaging of an
animal in each of the cavities.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be better understood with reference to the
following detailed description together with the appended
illustrative drawings in which like elements are numbered the
same:
FIGS. 1A-K depict two different loop detector elements of this
invention, a fabrication method, expanded views of portions of the
structure showing built in capacitors and a corresponding circuit
diagram;
FIGS. 2A&B depict a single saddle loop or coil (A) of this
invention and a tube made by placing mating saddles together
(B);
FIGS. 3A&B depict a preferred embodiment of birdcage type MRI
coil array of this invention;
FIGS. 3C&D depict another preferred embodiment of birdcage type
MRI coil array of this invention;
FIGS. 4A&B depict a preferred embodiment of a mixed
metal/superconductor MRI resonator of this invention;
FIGS. 4C&D depict another preferred embodiment of a mixed
metal/superconductor MRI resonator of this invention;
FIG. 4E depicts a schematic diagrams corresponding to the
resonators of FIGS. 4A-D;
FIGS. 5A&B depict a preferred birdcage-type hybrid coil array
resonator of this invention;
FIGS. 5C-E depict another preferred birdcage-type hybrid coil array
resonator of this invention;
FIGS. 6A&B depict another preferred birdcage-type hybrid coil
array resonator of this invention;
FIGS. 7A&B depict another preferred birdcage-type hybrid coil
array resonator of this invention;
FIGS. 8A&B depict a preferred small animal MRI apparatus of
this invention;
FIG. 9 depicts another preferred small animal MRI apparatus of this
invention;
FIG. 10 depicts another preferred small animal MRI apparatus of
this invention; and
FIGS. 11A-D depict physical characteristics of the coils resonators
of this invention.
FIG. 12A depicts performance of a circuit having the tuning and
matching circuitry within the small animal device and cooled
simultaneously producing improved SNR.
FIG. 12B depicts the tuning and matching circuitry for use with the
coils and arrays of this invention.
DETAILED DESCRIPTION OF THE INVENTION
The inventors have discovered that a new small animal or
multi-small animal MRI apparatus can be designed that has an
improved signal-to-noise ratio. The apparatus includes one or more
small animal tubes designed to receive a small animal and at least
one MRI coil or coil array associated therewith each tube. In one
preferred embodiment, the coils or coil arrays are fabricated
solely from superconducting materials and dielectric materials. In
another preferred embodiment, the coils or coil arrays are
fabricated from superconducting materials, metallic conducting
materials and dielectric materials. The apparatuses also include a
cryogenic cooling system. The multi-animal versions of these
apparatus provide improved MRI images simultaneously for all the
animals within the multiple animal apparatus.
The present invention broadly relates to an MRI coil or an array of
MRI coils. Each coil includes a plurality of inductive elements,
where each inductive element is formed of a superconducting layer
deposited on a dielectric substrate or a metallic conducting layer
or member. Each coil also includes an equal plurality of built-in
capacitive elements interconnecting adjacent pairs of the inductive
elements, where each capacitive element is formed from two
superconducting layers with a dielectric layer interposed
therebetween or a superconducting layer and a metallic conducting
layer with a dielectric layer interposed therebetween. The coils
can be rectangular in shape, circular in shape or elliptical in
shape and can be flat, curved or curvilinear.
The present invention also broadly relates to a small animal MRI
apparatus including at least one small animal cavity or tube
designed to receive a small animal. Each tube includes an effective
number of MRI coils or coil arrays sufficient to provide adequate
MRI data about the animal or animals in the apparatus. The
apparatus also includes a cryogenic cooling unit for maintaining
each coil or array in a superconducting condition. The apparatus
preferably includes multiple cavities, each cavity with coils or
arrays so MRI data can be acquired from each animal
simultaneously.
The present invention also broadly relates to method for acquiring
MRI data on multiple small animals including the step of placing
one or more small animals in the multiple small animal apparatus of
this invention. After placing the animals in the apparatus, the
small animal MRI apparatus is positioned within an MRI apparatus.
The MRI coils or arrays within the apparatus are then Cooled to a
superconducting state. MRI data is then collected simultaneously
from each of the animals in the apparatus.
A significant improvement of the signal-to-noise ratio (SNR) for
magnetic resonance imaging (MRI) applications, in which the thermal
noise of the rf receiver probe dominates the system noise, can be
achieved either by cooling a normal metal probe or by using
superconductors. The noise in an MRI system is primarily due to
thermal noise in the receiver coil and body, which is described by
the Nyquist formula:
V.sub.n=4k(T.sub.bR.sub.b+T.sub.cR.sub.c).DELTA.f, where k is
Boltzman's constant, T.sub.b and T.sub.c represent the body and
coil temperatures, respectively, and .DELTA.f is the bandwidth of
the receiver.
MRI is a widely used diagnostic tool, that provides unsurpassed
ability to image soft tissue. In MRI, the subject is placed in a dc
magnetic field, a sequence of magnetic field gradients and rf
excitation pulses are then applied to the subject, and relaxing
nuclei (usually protons) produce weak decaying rf signals that are
detected by an rf receiver probe. Such signals are weak due to the
small differences in energy level populations of parallel and
anti-parallel spins nuclei, (about 6 ppm at 1.5T) that contribute
to the signal. In both research and clinical MRI, there is a need
for high resolution and/or fast scan imaging, and the
signal-to-noise ratio (SNR) is the main limitation on fulfilling
these requirements. This makes the overall SNR the most important
parameter of MRI systems.
Noise in the system, in general, is created by conductive losses in
the probe and in the body. There are two regimes of such conductive
losses in MRI system. In the first regime, the loss in the body
dominates, so the SNR is primarily body loss dependent. While, in
the second regime, the loss in the coil dominates, so the SNR is
primarily coil loss dependent. In the body-loss dependent regime,
there is little advantage in reducing ohmic coil loss. However, in
the coil loss dependent regime, it has long been recognized that
cooling the probe reduces coil noise, and, therefore, can
significantly increase the SNR of the measurements.
The discovery and development of high-temperature superconducting
(HTS) materials has resulted in several attempts to build practical
probes with improved SNR. Indeed, preliminary studies have shown
that for selected applications, where the MRI system noise is in
the coil loss regime (low-field MRI, high-field microscopy, and
small-volume MRI), HTS MRI receiver coils perform significantly
better than comparable copper coils. HTS thin films are very
attractive for use in surface receiver coils, because such films at
77 K exhibit an extremely low surface resistance Rs (about 150
.mu.W at 10 MHz). This low surface resistance is several orders of
magnitude lower than the surface resistance of copper at the same
frequency and temperature. In addition, HTS materials have
relatively high critical temperature which can simplify cryostat
design and affords for a short distance between the superconducting
coil and the body or body part of the imaged.
One limitation when using surface probes for human imaging is their
relatively small field of view. As previously mentioned, phased
arrays can be used to allow small coils to cover a large region of
interest, while preserving the improved SNR. Recently, the use of
arrays has been complemented by elucidating optimal data
combinations. For example, a set of weighting coefficients are
derived, by which each pixel of each image is weighted in order to
achieve an optimal combination. The limit of operation may not be
defined solely by SNR, but may also have contributions from the
time available for image acquisition in such techniques as
functional brain imaging, real-time cardiac MRI, and pediatric
MRI.
Until recently, increases in MRI acquisition speed was limited by
the speed at which the field gradients could switched. However, the
hardware speed has increased to the point where the main
limitations are now physiological. Faster gradient switching used
for imaging and/or applying more rf power per unit time cause nerve
stimulation and heating, respectively. To overcome these
limitations, two new techniques, known as SMASH (SiMultaneous
Acquisition of Spatial Harmonics) (see D. K. Sodickson, W. J.
Manning, "Simultaneous acquisition of spatial harmonics (SMASH);
fast imaging with rf coils," Magn. Reson. Med. vol. 38, pp.
591-603, 1997) and SENSE (SENSitivity Encoding) (see K. P.
Prussman, M. Weigner, M. B. Scheidegger, and P. Boesiger, "SENSE:
sensitivity encoding for fast MRI," Magn. Reson. Med., vol. 42, pp.
952-962, 1999), have been developed and successfully demonstrated
in a number of applications. These two techniques and their
variants provide faster imaging by using known arrays of receiver
coils, but they also make use of the unique sensitivity profiles of
elements of a receiver array in order to complement the spatial
encoding generally accomplished through repeated application of
phase encoding magnetic field gradients.
As the number of array elements increases and their size continues
to decrease, conductive losses become more dominant. These losses
can overwhelm any SNR gains expected from use of smaller coils that
express less body noise. The use of cryogenically cooled copper/HTS
coils can extend the depth at which SNR gains can be achieved
through phased array acquisition. The potential SNR gain using
large arrays increases with the number of elements: SNR gain goes
up significantly when a single coil (N=1) is replaced with four
coils (N=4), and it increases even more for N=8 or N=16 arrays.
Thus, the potential advantage of cryogenically cooled//HTS receive
arrays with a large number of elements becomes even greater. These
SNR gains can be used alongside parallel imaging to achieve higher
accelerations while preserving maximum available image SNR.
Properly designed rf receiver coils are sensitive to rf magnetic
fields, while being substantially insensitive to rf electric
fields. That is why an MRI coil is always designed to form a rf
resonator.
Our invention includes designs of both superconducting single coil
resonators and coil array resonators and hydride single coil and
coil array resonators. Superconducting coil in either surface coil
or volume coil configuration is formed out of four or more sections
of dielectric/superconductor or dielectric/metal strips. Strips are
made out of thin HTS or metal thin films deposited on dielectric
rigid or flexible substrates. Such strips are connected together
via in build capacitors. At each of the connection YBCO layers and
separated them dielectric layer form a capacitor. Resonant
frequency is determined mainly by length of the structure and
separating YBCO layers dielectric thickness and dielectric
constant. Both surface flat, saddle coils and volume birdcage coils
were designed. Birdcage radiofrequency coils have been widely used
in magnetic resonance imaging because of their efficiency and
azimuthal B1 field homogeneity and design of all superconducting
birdcage for small animals has a practical potential. In the
invention both single coil and phased array configurations are
described. In addition, an idea for multi-animal simultaneous
measurement set up is shown for both flat and birdcage-like
superconducting arrays. A small cryogenic system for cooling down
superconducting coils is also shown.
Suitable Materials
Suitable dielectric material for use in this invention include,
without limitations, any dielectric material compatible with the
superconductors or metallic conductors used to fabricate the MRI
coils or coil arrays of this invention. Exemplary examples include,
without limitation, SiO.sub.2, Si.sub.3N.sub.4, Al.sub.2O.sub.3,
Y.sub.2O.sub.3, La.sub.2O.sub.3, Ta.sub.2O.sub.5, TiO.sub.2,
HfO.sub.2, ZrO.sub.2, or the like or mixture or combinations
thereof.
Suitable superconducting material for use in this invention
include, without limitations, any high temperature superconducting
material capable of being deposited using well known thin film
deposition techniques. Preferred high temperature superconducting
materials include, without limitation, high temperature
superconducting materials having a T.sub.c above a temperature of
liquid nitrogen or liquid carbon dioxide. One preferred class of
superconducting materials include, without limitations, high
temperature cuperate superconductors. Exemplary examples of
cuperate superconductors include, without limitation,
YBa.sub.2Cu.sub.3O.sub.7, La.sub.2-xBa.sub.xCuO.sub.4,
La.sub.2-xSr.sub.xCuO.sub.4, La.sub.2-xSr.sub.xCaCuO.sub.4,
Bi.sub.2Sr.sub.2Ca.sub.2Cu.sub.3O.sub.10,
Tl.sub.2Ba.sub.2Ca.sub.2Cu.sub.3O.sub.10,
Hg.sub.0.8Tl.sub.0.2Ba.sub.2Ca.sub.2Cu.sub.3O.sub.8.33,
HgBa.sub.2Ca.sub.2Cu.sub.3O.sub.8,
HgBa.sub.2Ca.sub.3Cu.sub.4O.sub.10+,
HgBa.sub.2Ca.sub.1-xSr.sub.xCu.sub.2O.sub.6+,
HgBa.sub.2CuO.sub.4.sup.+, TlBa.sub.2Ca.sub.2Cu.sub.3O.sub.9+,
Tl.sub.2Ba.sub.2Ca.sub.2Cu.sub.3O.sub.10,
Tl.sub.1.6Hg.sub.0.4Ba.sub.2Ca.sub.2Cu.sub.3O.sub.10+,
Tl.sub.0.5Pb.sub.0.5Sr.sub.2Ca.sub.2Cu.sub.3O.sub.9,
Tl.sub.2Ba.sub.2CaCu.sub.2O.sub.6,
TlBa.sub.2Ca.sub.3Cu.sub.4O.sub.11, TlBa.sub.2CaCu.sub.2O.sub.7+,
Tl.sub.2Ba.sub.2CuO.sub.6,
Bi.sub.1.6Pb.sub.0.6Sr.sub.2Ca.sub.2Sb.sub.0.1Cu.sub.3O.sub.y,
Bi.sub.2Sr.sub.2Ca.sub.2Cu.sub.3O.sub.10,
Bi.sub.2Sr.sub.2CaCu.sub.2O.sub.9,
Bi.sub.2Sr.sub.2Ca.sub.0.8Y.sub.0.2Cu.sub.2O.sub.8,
Bi.sub.2Sr.sub.2CaCu.sub.2O.sub.8,
AuBa.sub.2Ca.sub.3Cu.sub.4O.sub.11,
AuBa.sub.2(Y,Ca)Cu.sub.2O.sub.7, AuBa.sub.2Ca.sub.2Cu.sub.3O.sub.9,
NdBa.sub.2Cu.sub.3O.sub.7, GdBa.sub.2Cu.sub.3O.sub.7,
YBa.sub.2Cu.sub.3O.sub.7, Y.sub.2Ba.sub.4Cu.sub.7O.sub.15,
TmBa.sub.2Cu.sub.3O.sub.7, YbBa.sub.2Cu.sub.3O.sub.7,
Sn.sub.2Ba.sub.2(Y.sub.0.5Sr.sub.0.5)Cu.sub.3O.sub.8,
La.sub.2Ba.sub.2CaCu.sub.5O.sub.9+, (Sr,Ca).sub.5Cu.sub.4O.sub.10,
Pb.sub.2Sr.sub.2(Y,Ca)Cu.sub.3O.sub.8,
GaSr.sub.2(Y,Ca)Cu.sub.2O.sub.7,
(In.sub.0.3Pb.sub.0.7)Sr.sub.2(Ca.sub.0.8Y.sub.0.2)Cu.sub.2O.sub.x,
(La,Sr,Ca).sub.3Cu.sub.2O.sub.6, La.sub.2CaCu.sub.2O.sub.6+,
(Eu,Ce).sub.2(Ba,Eu).sub.2Cu.sub.3O.sub.10+,
(La.sub.1.85Sr.sub.0.15)CuO.sub.4, SrNdCuO, (La,Ba).sub.2CuO.sub.4,
(Nd,Sr,Ce).sub.2CuO.sub.4, Pb.sub.2(Sr,La).sub.2Cu.sub.2O.sub.6,
(La.sub.1.85Ba.sub.0.15)CuO.sub.4, or the like, or mixtures or
combinations thereof.
Suitable metallic material for use in this invention include,
without limitations, copper, silver, gold, platinum, other noble
metals, alloys thereof, or mixture or combinations thereof.
Fully Superconducting Coils
Referring now to FIGS. 1A-C, a preferred embodiment of a
substantially rectangular, superconducting MRI coil or loop
apparatus of this invention, generally 100, is shown to include
four superconducting films 102 deposited on four dielectric strips
104. The strips 104 are arranged into the substantially rectangular
coil 100 so that the superconducting films 102 face each other at
overlapping end portions 106. At the end portions 106, dielectric
films 108 are interposed between facing superconducting film
portions 110. The overlapping end portions 106 form built in
capacitors electronically interconnecting superconducting inductive
portions 112 of the films 102.
Alternatively, looking at FIGS. 1D-F, another preferred embodiment
of a superconducting coil device of this invention, generally 100,
is shown to include four superconducting films 102 deposited on
four dielectric strips 104. The strips 104 are arranged into the
substantially rectangular coil 100 so that the superconducting
films 102 face up forming built in capacitors at overlapping end
portions 106, which electronically interconnect superconducting
inductive portions 112 of the films 102.
Referring now to FIGS. 1G-H, a manufacturing process for forming
the loops or coils of FIG. 1A-F is shown. A superconducting film
ring 102 is deposited onto a circular substrate 104. Then films of
dielectric 114 are deposited on top of portions 116 of the film
102. Then small superconducting films 118 are deposited on top of
the portions 120 of the dielectric films 114. The coils can be
fabricated using, for example, a multi-target pulsed laser
deposition technique and standard photolithography or ion
milling.
One primary coil design parameter is the filling factor, which
indicates how much of the coil's shape is adjusted to accommodate a
shape of a body for which the coil is intended. HTS technology, in
principle, requires flat epitaxially polished dielectric substrates
and as a result such HTS MRI coils have different coil-body
distances in the coil's center than at their edges. To overcome
this deficiency, the apparatuses of the present invention are
fabricated by depositing sections of HTS films on very thin
flexible dielectric substrates. Such deposition is possible using
an ion beam assisted deposition technique or a variant of ion beam
assisted deposition.
Referring now to FIGS. 1I-J, two constructions for attaching the
coils of this invention to the outside world are shown. Looking at
FIG. 1I, one construction 150 includes a substrate 152 having
deposited thereon a first film 154 of superconducting material.
Deposited on the top of the film 154 is a dielectric film 156. And
deposited on the dielectric film 156 is a second film 158 of
superconducting material. The construction 150 also includes a
metal pad 160 having bonded thereto a wire 162 for communication
with the an MRI instrument. Looking at FIG. 1J, another
construction 164 includes a bottom film 166 of a superconducting
material, a top film 168 of a superconducting material and a
dielectric film 170 interposed therebetween. The construction 164
also includes a wire 172 bonded to the metal pad metal pad 174
deposited on the a top film 168.
Referring now to FIG. 1K, an electrical schematic 180 is shown that
is the electrical equivalent of the coils constructions of FIGS.
1A-H. The schematic 180 includes four inductors 182 interconnected
by four capacitors 184. Depending on the inductance of the
inductors and the capacitance of the capacitors, the coils forms a
resonance circuit, which is capable of transmitting and receiving
RF signals corresponding to resonances of magnetically active
nuclei.
Fully Superconducting Curvilinear Coils
Referring now to FIG. 2A, a preferred embodiment of a saddle or
curvilinear loop or coil of this invention, generally 200, is shown
to include two straight members 202, where each straight member 202
comprises a superconductor film 204 deposited on a rigid dielectric
substrate 206. The saddle coil 200 also includes two curved member
208, where each curved member 208 comprises a plurality of
superconducting film sections 210 deposited on a flexible
dielectric substrate 212. The saddle coil 200 also includes four
capacitors 214 formed from overlapping regions 216 of the two
straight members 202 and the two curved members 208. At the
overlapping regions 216, dielectric films 218 are formed to
separate an end portion 220 of the superconducting films 204 from
end superconducting film sections 222 of the curved members 208. If
the straight members 202 are flipped over, then the dielectric
films 218 are not needed as was shown in FIGS. 1D-F. Of course,
depending on the deposition technique used to form the
superconducting films, the film could be formed without being
formed of separated sections, where each section is flat and not
curves.
Birdcage-Type Resonator Using Curvilinear Coils
Looking at FIG. 2B, a preferred embodiment of an animal MRI or
birdcage apparatus 224 is shown to include two saddle coils 200
arranged in a closed configuration forming an animal cavity 226. In
such a closed configuration, the saddles 200 work either as a
single coil or an array of two coils. Preferably, the
superconductors are high temperature superconductors such as a YBCO
superconductors. However, any other high temperature superconductor
can be used as well. It should be recognized that the resonance
frequency of the coils 200 are controlled by well known factors
such as the dielectric used, the thickness of the superconducting
and dielectric layers, the diameter of curvature to name a few and
one of ordinary skill in the art can adjust these parameters to
form coils having a desired shape and desired resonance
frequency.
Fully Superconducting Birdcage-Type Resonators
Referring now to FIGS. 3A&B, another preferred embodiment of an
all superconducting birdcage apparatus, generally 300, is shown to
include eight straight members or legs 302, where each straight
member 302 comprises an outer rigid dielectric substrate film 304,
an inner dielectric film 306 and a superconductor film 308
interposed therebetween. The birdcage 300 also includes four
circular members 310, where each curved member 310 comprises a
superconducting film 312 deposited on a flexible dielectric
substrate 314. As in the birdcage of FIGS. 2A&B, the
superconducting film 312 is preferably fabricated as a plurality of
substantially flat section; however, as fabrication techniques
progress, the superconducting film 312 may eventually be of a
fabricated curvilinear form. The legs 302 and the circular members
310 are configured to form a generally cylindrical animal cavity
316. The legs 302 and circular or arcuate members 310 overlap at
first and second overlap regions 318 and 320, each overlap region
318 or 320 forms a capacitor interconnecting inductors formed by
the superconducting films. This design forms a low-pass birdcage
resonator. The flexible dielectric substrates are generally between
about 30 and about 50 thick and formed of yttrium, strontium,
zirconium dielectric or a sapphire dielectric film. The inner
dielectric film is generally teflon, other polymers, silica
titanate or similar dielectric materials.
Referring now to FIGS. 3C&D, another preferred embodiment of an
all superconducting birdcage apparatus, generally 300, is shown to
include four straight members or legs 302, where each straight
member 302 comprises an outer rigid dielectric substrate film 304,
an inner dielectric film 306 and a superconductor film 308
interposed therebetween. The birdcage 300 also includes four
circular or arcuate members 310, where each curved member 310
comprises a superconducting film 312 deposited on a flexible
dielectric substrate 314. As in the birdcage of FIGS. 2A&B, the
superconducting film 312 is preferably fabricated as a plurality of
substantially flat section; however, as fabrication techniques
progress, the superconducting film 312 may eventually be of a
fabricated curvilinear form. The legs 302 and the circular members
310 are configured to form a generally cylindrical animal cavity
316. The legs 302 and circular or arcuate members 310 overlap at
overlap regions 318, each overlap region 318 forms a capacitor
interconnecting inductors formed by the superconducting films in
the legs. The apparatus 300 also includes four arcuate sections 320
interlaced with the legs 304, where the sections 320 form
capacitors interconnecting inductor form by the arcuate members
310. The four legged apparatus forms a band-pass birdcage
resonator, where the capacitors are placed not only on the legs,
but also on the ring. The four flat strips comprise a
YBCO/substrate composite and the four flexible strips comprises a
YBCO/buffer-layer/flexible ZrO.sub.2 composite to form a four legs
band-pass birdcage resonator.
Hybrid Coils
In order to accommodate requirements for usually complicated shapes
of optimized MRI coils as well as to allow relatively easy cooling
of HTS coils, we have also designed hybrid (HTS/cooper) MRI coils
or arrays. Referring now to FIGS. 4A&B, a preferred mixed
superconducting-metal coil of this invention, generally 400, is
shown to include two copper blocks 402 and two legs 404, where each
leg 404 includes a dielectric substrate layer 406 and a
superconducting layer 408 deposited thereon. The blocks 402 are
positioned at end portions 410 of the legs 404 with the
superconducting layer 408 of the legs 404 facing the copper blocks
402. The coil 400 also includes dielectric strips 412 interposed
between the copper blocks 402 and end portions 414 the
superconducting layer 408 of the legs 404. The coil 400 also
includes metal pads 416 formed on end portions 418 of the
dielectric layers 406 of the legs 402. The copper blocks 402,
dielectric strips 412 and the end portions 414 of the
superconducting layers 408 combine to form built-in internal
capacitors interconnecting the copper blocks 404 and the
superconducting layers 408. The end portions 414 of the
superconducting layers 408, the end portions 418 of the dielectric
layers 406, and the metal pads 416 form built-in external
capacitors.
Referring now to FIGS. 4C&D, another preferred mixed
superconducting-metal coil of this invention, generally 400, is
shown to include two copper blocks 402 and two legs 404, where each
leg 404 includes a dielectric substrate layer 406 and a
superconducting layer 408 deposited thereon. The blocks 402 are
positioned at end portions 410 of the legs 404 with the dielectric
substrate layer 406 of the legs 404 facing the copper blocks 402.
The coil 400 also includes dielectric strips 412 formed on end
portions 414 the superconducting layer 408 of the legs 404 and
metal tabs 416 formed on the dielectric strips 412. The copper
blocks 402, end portions 418 of the dielectric layer 406, and the
end portions 414 of the superconducting layers 408 combine to form
built-in internal capacitors interconnecting the copper blocks 404
and the superconducting layers 408. The end portions 414 of the
superconducting layers 408, the dielectric strips 412, and the
metal tabs 416 form built-in external capacitors.
The main concept of these mixed or composite coils are the same as
in the fully superconducting coils of FIGS. 1A-F; however, two
sections of the HTS films are replaced with copper blocks allowing
the coils to be directly cooled by a cooling system, i.e., the
copper or other metallic blocks can be placed in direct contract
with a cooled surface. As with the fully superconducting coils, the
mixed or composited coils of FIGS. 4A-D include built in capacitors
using two conducting layers separated by a dielectric layer.
Referring now to FIG. 4E, an equivalent circuit, generally 450, is
shown that corresponds to the coils of FIGS. 4A-D. The circuit 450
includes inductors 452 interconnected by internal capacitors 454
and capacitively isolated from external electronic components by
external capacitors 456. The circuit 450 also includes a virtual
ground plane 458.
The hybrid MRI resonators of this invention include two sections of
YBCO/substrate and two pieces of copper which are interconnected
via the built-in internal capacitors 454. Two of the metal pads 416
are adapted to couple the resonator to a scanner amplifier, while
the other two metal pads 416 are adapted to decouple adjacent
resonators if the individual coils are used in an array
configuration. Two ways of creating capacitors are shown. As shown
in FIGS. 4A&B, the built-in internal capacitors 454 comprise
the copper block 402/the dielectric strip 412/the superconducting
layer 408 such as a YBCO layer. As shown in FIGS. 4C&D, the
built-in internal capacitors 454 comprise the copper block 402/the
dielectric substrate layer 406/the superconducting layer 408 such
as a YBCO layer. The built-in internal capacitors 454 in
conjunction with the conductive elements which for the inductors
452 for the coil resonator, while the built-in external capacitors
456 interconnect metal and superconducting films into single loop
(resonator). The external capacitors 456 are designed to either
connect the resonator to an amplifier or for decoupling array
elements.
Birdcage-Type Resonators Using Hybrid Coils
Referring now to FIGS. 5A&B, a preferred embodiment of a mixed
superconducting-metal birdcage array resonator, generally 500, is
shown to include twelve hybrid coils 502 as shown in FIGS. 4A&B
arranging in a circular configuration forming a cavity 504. In the
coils 502, the copper blocks 402 include a portion 506 that extends
out past the coils layers 406, 408, 412, and 416. The portions 506
are designed to directly contact a cold inner surface 508 of a
metal ring 510 that would be in contact with a coolant on its outer
surface 512. The resonator 500 forms a cylinder having a cavity
into which a small animal can be placed and the assembly then
placed in an MRI device. The resonator 500 is cooled by bring the
outer surface of the metal ring 510 in contact with a coolant, such
as liquid nitrogen. The resonator 500 is an example of phased array
made out of hybrid (metal/superconductor) resonators of FIGS. 4A-D.
The individual coils 502 can be mutually de-coupled, as it is
required for phased array use via the built-in capacitors and wires
leading from the metal pads from one coil to the next or from a
coil to a pre-amplifier or amplifier associated with the MRI
device. Although an outer metal ring, preferably a copper ring, is
shown in FIG. 5B, the ring can be constructed out of any good heat
conductor, metal or non-metal. Preferred non-metal rings can be
made out of polycrystalline sapphire or other non-metal thermal
conducting materials.
Referring now to FIGS. 5C&D, another preferred embodiment of a
mixed superconducting-metal birdcage array resonator, generally
550, is shown to include two thermal conducing members 552 (only
one shown), each member 552 including a circular aperture 554
therethrough having twelve equally spaced, circularly configured
protrusions 556 extending into the aperture 554. On each lateral
side 558 of each protrusion 556 are placed legs 560 extending
between the two members 552 to form an elongate resonator where the
aperture 554 comprises the small animal cavity. Looking from the
protrusions 556 out, each leg 560 includes an inner, rigid
dielectric substrate layer 562 in contact with a side 558 of a
protrusion 556 and a superconducting layer 564. These two layer 562
and 564 extend between the two member 552. Each leg 560 also
includes a dielectric strip 566 formed on or in contact with an end
portion 568 of the superconducting layer 564. Each dielectric strip
566 in turn has deposited thereon or is in contact with a metal pad
570. The metal pads 570 can have a wire 572 bonded thereto by a
soldier bump 574 so that the individual coils can be formed into an
array and/or connected to pre-amplifiers or amplifiers associated
with the MRI device. The resonator 550 can also include climps 576
designed to hold the two legs 560 per protrusion against the
protrusions 556. The member 552 are designed to directly contact a
coolant on their outer surfaces 578. The resonator 550 forms a
cylinder having a cavity into which a small animal can be placed
and the assembly then placed in an MRI device. The resonator 550 is
cooled by bring the outer surfaces 578 of the members 552 in
contact with a coolant, such as liquid nitrogen. The resonator 550
is an example of phased array made out of hybrid
(metal/superconductor) coils. The individual coils 502 can be
mutually de-coupled, as it is required for phased array use via the
built-in capacitors and wires leading from the metal pads from one
coil to the next or from a coil to a pre-amplifier or amplifier
associated with the MRI device. The members 552 are preferably made
out of copper, but other metal will work, especially metals having
a high thermal and electric conductivities.
Referring now to FIG. 5E, a schematic corresponding to the hybrid
arrays of FIGS. 5A-D is shown to include the coil capacitors C and
coil inductors L along with coupling, decoupling, tuning and
matching elements CC, DC and CM. The outputs O/P are forwarded to
preamps that can be either within the cooled area or external
thereto. The coupling, decoupling, tuning and matching elements can
be similarly applied to any array of MRI coils of this inventor or
to any single MRI coil of this invention.
Referring now to FIGS. 6A&B, another preferred embodiment of a
mixed superconducting-metal birdcage resonator of this invention,
generally 600, is shown to include a metallic tube 602 having
formed on an outer surface 604 of the tube 602 two curvilinear
superconducting layers 606 and two straight superconducting layers
608. The curvilinear layers 606 are disposed radially across end
portions 610 of the tube 602, while the straight layers 608 run
axially from end portions 612 of the curvilinear layers 608. At
their overlapping regions 614 and 616, a layer 618 of mica or other
dielectric material is interposed therebetween. These overlapping
regions form built-in capacitors interconnecting inductive elements
formed by the non-overlapping 620 of the superconducting layers 606
and 608.
Referring now to FIGS. 7A&B, another preferred embodiment of a
mixed superconducting-metal birdcage array resonator, generally
700, is shown to include two metallic rings 702 and two straight
superconducting legs 704 connecting the rings 702 at opposite sides
of each ring 702 at flattened sections 706 with a dielectric layer
707 interposed between the flattened section 706 of the rings 702
and overlapping portions 708 of the legs 704.
In FIGS. 6A&B and 7A&B, the dielectric layer or mica layer
is generally about 20 .mu.m thick. The ring or tube is generally
about 10 mm thick and about 2'' long and about 2.5'' in diameter.
The resonators resonate at a frequency of about 200 MHz. Of course,
the resonate frequency can be changed by changing the capacitance
of the built-in capacitors and the inductance of the inductive
regions of the superconducting layer and metallic layers.
Referring now to FIGS. 8A&B, a preferred small animal MRI
resonator apparatus, generally 800, is shown to include a plastic
or non-magnetic cryostat housing 802 having a cylindrical aperture
804 therethrough defining a small animal cavity. Surrounding the
aperture 804, is a cylindrical MRI resonator 806 of this invention
in thermal contact with a thermally conductive plate 808. The plate
808 comprises the outer surface of a liquid nitrogen reservoir 810.
The housing 802 also includes a ring sealing member 812 having two
electrical feed tube 814 extending therethrough. The housing 802 is
capable of being placed under a vacuum. The cryostat 800 includes a
vacuum shroud 802, a liquid nitrogen container 810 with one side
wall made out of a sapphire plate 808. The container 810 includes a
liquid nitrogen inlet 816 and a liquid nitrogen outlet 818. The
plate temperature will be uniformly at 77K and will not dependent
on level of liquid nitrogen in the container 810. The MRI resonator
806 comprises copper and/or YBCO materials and will be in thermal
contact with the plate 808. In this apparatus 800, the aperture 804
can either extend the entire length of the housing or it can stop
at the plate 808 so that the small animal is confined within the
part of the apparatus 800 surrounded by the resonator 806.
Referring now to FIG. 9, another preferred small animal MRI
resonator apparatus, generally 900, is shown to include four hybrid
arrays 902 of FIGS. 5A-D, each array 902 defining having a small
animal cavity 904. The four arrays 902 are housed in a vacuum
shroud or housing 906 and are in thermal contact with a plate 908
which forms an outer surface of a liquid nitrogen reservoir (not
shown). The housing 906 includes a top (not shown) that seals the
housing 906 so that the interior can be evacuated, where the top
includes electrical wiring feed throughs as described previously.
The apparatus 900 can accommodate up to four animals and MRI data
can be acquired on each simultaneously or separately.
Referring now to FIG. 10, another preferred small animal MRI
resonator apparatus, generally 1000, is shown to include a
non-conductive housing 1002 having four small animal tubes 1004.
The housing 1002 also includes eight flat MRI coil or MRI array
apparatuses 1006, where each tube 1004 is adjacent three MRI
apparatuses 1006. The eight MRI apparatuses 1006 are in thermal
contact with a thermally conducting plate 1008 which forms an outer
surface of a liquid nitrogen reservoir (not shown). The housing
1002 includes a top (not shown) that seals the housing 1002 so that
the interior can be evacuated, where the top includes electrical
wiring feed throughs as described previously. The apparatus 1000
can accommodate up to four animals and MRI data can be acquired on
each simultaneously or separately. The rigid flat MRI apparatuses
1006 comprise preferably HTS coils and by sharing coils, a reduced
number of HTS coils are needed for such systems. Each tube in which
a mouse is placed is surrounded by array of superconducting
coils.
Referring now to FIGS. 11A-D, illustrate the physical
characteristic so MRI coils and arrays made thereform. Looking at
FIGS. 11A&B, the magnetic fields generated by the coils of this
invention are shown. Looking at FIGS. 11C&D, the SNR for these
coils is shown.
The inventors have found that when tuning and matching circuitry is
placed next to the superconducting array and cooled together with
the array, the entire system has superior performance. In fact,
cooling the two circuit elements together is preferred because it
allow us to take advantage of the high Q of the arrays of this
invention. The inventors have also found that by integrating a
pre-amplifier into this circuitry so that the pre-amp is cooled as
well results in further noise reduction. Looking at FIGS.
12A&B, the performance of a circuit having the tuning and
matching circuitry within the small animal device and cooled
simultaneously produces improved SNR. FIG. 12B also shows the
tuning and matching circuitry for a coil similar to the coils of
this invention disclosed in PCT Application Serial No.
PCT/US03/33933, filed 24 Oct. 2003, published as WO04038431,
incorporated herein by reference. The tuning and matching circuitry
shown in FIG. 12B can be use with the coils and arrays of this
invention as well. Co-cooling the matching and tuning circuitry,
applies, in general, not only to thin film arrays, but also to
saddle, birdcage and hybrid coils/arrays. In fact, we have
installed such low temperature circuit in our cryostat, which
designing idea is presented in the provisional.
All references cited herein are incorporated by reference. While
this invention has been described fully and completely, it should
be understood that, within the scope of the appended claims, the
invention could be practiced otherwise than specifically described.
Although the invention has been disclosed with reference to its
preferred embodiments, from reading this description those of skill
in the art can appreciate changes and modifications that may be
made which do not depart from the scope and spirit of the invention
as described above and claimed hereafter.
* * * * *